The term polyphenylene ether resin is well known to those skilled in the art as a class of thermoplastic materials having excellent physical properties such as dimensional stability, dielectric characteristics, and they are made by a variety of processes from the corresponding phenols.
Some of the polyphenylene ethers are disclosed in the prior art patent literature e.g., Hay U.S. Pat. Nos. 3,306,874, and 3,306,875 and Nakashio et al. U.S. Pat. No. 3,573,257 and the like.
Blends of a polyphenylene ether and a styrene resin are also well known to those skilled in the art and are disclosed in numerous patent literature.
Cizek U.S. Pat. No. 3,383,435 discloses polyphenylene ether/rubber modified styrene resin compositions, wherein the rubber component being unsaturated type such as polybutadiene.
Nakashio et al. U.S. Pat. No. 3,658,495 discloses polyphenylene ether/rubber modified styrene resin compositions wherein the rubber component being ethylene/alpha-olefin/polyene terpolymer.
Haaf U.S. Pat. No. 4,167,507 discloses blends of polyphenylene ether and a partially hydrogenated styrene/conjugated diene block copolymer such as Shell Chemical's Kraton G's.
Blends of polyphenylene ether and mineral fillers are well known and are disclosed in patent literature.
Lee Jr. U.S. Pat. No. 4,166,812 discloses blends of polyphenylene ether, rubber modified polystyrene and aluminosilicate filler.
Cooper et al. U.S. Pat. No. 3,959,211 discloses blends of polyphenylene ether, rubber modified polystyrene wherein the rubber component is ethylene-propylene-diene terpolymer, triphenyl phosphate, and mineral filler such as titanium dioxide.
Abolins et al. U.S. Pat. No. 4,373,052 discloses blends of polyphenylene ether, rubber modified polystyrene, triphenyl phosphate and talc filler.
Abolins U.S. Pat. No. 4,478,970 discloses blends of polyphenylene ether, triphenyl phosphate and clay filler. Thermoplastic compositions containing electro conductive materials such as metal flakes, metal fibers, carbon fibers, carbon blacks, or the combination thereof, have long been used for the purpose of rendering the plastic components fabricated therefrom electromagnetic interference shielding characteristics or providing plastic components with higher electroconductivity or antistatic electricity characteristics.
Cizek U.S. Pat. No. 3,383,435 teaches a blend of polyphenylene ether, polystyrene and carbon black.
Shilenko Soviet Pat. No. SU.376815 discloses a polyphenylene ether/carbon black composition.
Takenaka et al. U.S. Pat. No. 3,697,450 discloses blends of thermoplastics, electroconductive materials such as carbon black, graphite and metal powder or the combination thereof, and silicon containing mineral fillers such as silicon carbide, silica, glass powder and stone powder, and specifically discloses a blend of polyphenylene ether, carbon black and silica, the said composition having the volume resistivity of 1.2.times.10.sup.5 ohm.multidot.cm.
Although the patent discloses the combined use of carbon black and silicon containing inorganic fillers such as silicon carbide, silica, stone powder and the like inter alia, the combined use of carbon black and such inorganic fillers resulted in higher resistivity as compared with the use of carbon black alone as shown in TABLE I of the patent specification.
Moreover the combined use of carbon black and other silicon containing inorganic filler than silicon carbide, silica, or glass powder is not disclosed in any of the examples of the patent.
Abolins U.S. Pat. No. 4,404,125 discloses blends of polyphenylene ether, polystyrene and electroconductive materials selected from the group consisting of aluminum flake, a combination of aluminum flake with conductive carbon blacks or carbon fibers, a combination conductive carbon blacks and carbon fibers, and carbon fibers, but does not disclose the combined use of electroconductive material and inorganic filler. Plastic components having improved electromagnetic interference shielding characteristics/electroconductivity are widely used in the electric/electronics industry.
Illustrative examples of the component are personal computer housing, CRT display housing, faximile housing, IC chip tray and the like.
Polyphenylene ether resin compositions containing electroconductive material are also commonly used in the electric/electronics industry for these applications.
In making a thermoplastic composition having electromagnetic interference shielding/electroconductive characteristics, it is desirable to achieve a required level of the characteristics with lower content of electroconductive materials.
It has now been unexpectedly discovered that a polyphenylene ether composition containing a carbon black and a mineral filler exhibits higher electroconductivity than a polyphenylene ether/carbon black blend without a mineral filler therein.
It is therefore a primary object of this invention to provide a polyphenylene ether resin composition having improved electroconductivity, or reduced electroresistivity.
Another object of this invention is to provide molded articles of a polyphenylene ether resin composition having improved electromagnetic interference shielding characteristics and/or electroconductivity.
According to the present invention there are provided thermoplastic compositions having reduced electroresistivity comprising,
A) a polyphenylene ether resin and, PA1 B) optionally a styrene resin and, PA1 C) optionally impact strength improving amount of one or more of impact strength improvintg polymer(s) and, PA1 E) from about 5 parts to about 40 parts by weight of a carbon black based on the total of the polymers, A) the polyphenylene ether resin, B) the styrene resin, and C) the impact strength improving polymer and, PA1 F) optionally plasticizing amount of one or more of plasticizer(s),
D) from about 5 parts to about 20 parts by weight of at least one mineral filler selected from the group consisting of talc, mica, and wollastonite based on 100 parts by weight of the total of the polymers, A) the polyphenylene ether resin, B) the styrene resin, and C) the impact strength improving polymer and,
characterized in that the surface resistivity of the composition is lower than about 10.sup.10 ohm.
Other conventional additive such as flame retardants, stabilizers and the like may be suitably employed therein.